This invention relates to an improved refractometer and to a method for measuring the light refraction of liquids. As such, the refractometer is adapted for use by individual physicians and others having limited laboratory space.
The method and the device may be used for measuring the concentration of a dissolved solute. For example, the refractometer may be used in clinical testing of biological specimens. More particularly, the refractometer can be used to determine the specific gravity of urine. However, this particular use is an illustrative example, not a limitation, since the device and method of the present application are equally applicable to measuring sugar concentration and other dissolved solids in liquids.
Heretofore, there have been two primary methods for determining the specific gravity of urine. The first method employed a urinometer, a specially calibrated hydrometer. One problem with such hydrometers was that they required a large volume of the specimen, at least 30-40 ml. Moreover, the readings obtained were inherently somewhat inaccurate, due to the formation of a meniscus (or curved top line) along the reading column, the reading being done conventionally from the bottom of the meniscus. Also, since the urinometer readout was on an analog scale, it was therefore subject to operator error.
A second method of determining the specific gravity of urine has employed an American Optical refractometer, a device with the distinct advantage of requiring only two or three drops of specimen. There have been, however, several drawbacks in this device, one being that again, there is an analog readout with its potential operator error. Another drawback has been that the small optical chamber has had to be cleaned between each use: this necessity has added considerably to the time required to perform a series of tests. This prior refractometer has further required both a highpower optical system, a manual visual alignment, i.e., a knob had to be turned by the operator to align two fine lines to obtain a reading, and, again, this increased the potential for operator error.
Among the objects of the present invention is to overcome all of the above drawbacks. Another object is to provide such a device which is no more expensive to manufacture than the American Optical refractometer. Another object is to provide quicker and more accurate determination.
The present invention enables quantitative analysis of various body fluids and other liquids by measuring the displacement of a beam of monochromatic light.
An advantage of the present invention is that the time required to test a given sample is dramatically reduced to the point where up to ten specimens may be tested in one minute.
Another advantage of the present invention is that the possibility of operator error is greatly reduced, since measurement is automatic and the results are displayed digitally, eliminating the need for interpretation of a fine analog scale by the operator.
Another aspect of the digital refractometer of this invention is that erroneous readings caused by the use of too small a sample are eliminated by a novel actuation system which delays the taking of readings until sufficient sample has been used. Further, erroneous readings are prevented by imposing a time delay in taking the reading for a time sufficient to insure that any air bubble in the specimen will have dispersed.
Yet another advantage of the present invention is that only a small amount of specimen is required and no washing between samples is necessary for routine clinical testing.
A further advantage of the digital refractometer of this invention is that no high-power optical system is required, nor is any manual adjustment by the operator required in taking a reading.